(a) Field of the Invention
The invention relates to valve arrangements for connection of a hydraulic accumulator with a hydraulic machine such as a hydraulic pump or motor.
(b) Prior Art
Constructions are known in which a hydraulic machine able to be selectively operated as a pump converts surplus kinetic energy into potential energy by charging a high pressure or low pressure accumulator. This potential energy may then be utilized when required, for example, by driving the hydraulic machine as a motor.
Between the hydraulic machine and the pressure accumulator there is a shutoff valve which has to be completely leak-proof in order to ensure that there is no chance at any time of the hydraulic machine being acted upon by the pressure and thus caused to run, especially in the case of a positive displacement machine, since then such a leaking shutoff valve would cause such an accumulation of pressure in the course of time that the machine would be put into operation.
In the prior art such a shutoff valve has always been a hand-operated shutoff valve which was opened and shut when the need arose.
Such a hand-operated shutoff valve only makes a relatively coarse control possible, especially since every opening and closing operation is slow.
If such a pressure accumulator is mounted on a vehicle and it is to be used for operation of the vehicle, the use of such a hand-operated shutoff valve is quite out of the question, since its operation would be too much of a distraction for the driver.
In order to make possible an even more efficient use of the excess energy in a stationary plant or in a vehicle, especially when there has to be a frequent change in the mode of operation, it is necessary to integrate the shutoff valve in an automatic or other control system so that it is no longer controlled by hand but rather by control signals. As has been shown by tests undertaken by the assignee, the coupling of an actuator with a conventional shutoff valve does not lead to satisfactory results since the actuating force is excessive or the shutoff valve is too slow to switch from one setting to the other.
Since during operation, pressure in excess of 400 bar may occur at the shutoff valve, it is not possible to employ a conventional remote controlled spool valve, since it would not be sufficiently leak-proof and furthermore, dependent on the particular type, very high forces might be produced by it and then act on the actuator.